The "memory" is perfectly reliable; the problem is that it's powered by a watch battery that inevitably drains and has to be replaced regardless of whether the cart is being used. There is ample documentation on the battery replacement process.
The problem on second Pokémon generation was inclusion of the clock. SRAM is very frugal. My 1980s NES Zelda carts are still on the first batteries. They last literally decades holding the SRAM nonstop.
The clock on the other side needs way more power.
Nintendo absolutely knew what they were doing and that it was wrong. Many Game Boy (Color) titles contain CR1616 cells. Pokémon 2nd generation contain CR2025 which have triple(!) the capacity. They didn't include that big thing for no reason. Kid Icarus: Of Myths and Monsters, stamp on the CR1616 says year 1992 → Still okay. Pokémon lasted between 5 and 8 years on a three times more powerful battery.
They knew they would cause a lot of frustration or even tears with people losing saves of complex games containing a vast amount of randomness in creating saves (
"I lost my favorite Pokémon!")
Problem continues on third generation. SRAM has been replaced by 128KB flash which works after the battery is drained. Smaller GBA carts hold are back to the small CR1616 and lose the clock functionality relatively quickly with the game needing to be either deleted to restore clock functionality after battery swap or the save repaired by homebrew software in a DS Lite.
I was looking at doing that, but memory on those old cartridges isn't super reliable. Not something I'd be quick to buy as a gfit second hand, and I didn't own that particular version.
The SRAM on GBC games is very reliable. First games with save feature indeed had some trouble.
"Hold in the reset button while turning off the power." on NES Zelda and some others. Repeated turning off/on or abrupt power off could wipe SRAM.
I tried it on GBC games, especially Pokémon Crystal before playing the game (to see if it is reliable). I could never make the game lose or corrupt the save. Even turning off during saving (big no-no!) had no impact.
To finally reach the boarders of reliability I had to resort to using the Game Boy emulator within Pokémon Stadium 2 turning off the power interrupting save progress. Search for Celebi Egg Trick. Only way targeted corruption succeeded (on the 100th attempt).
If you regularly use a second generation Pokémon game you will notice when the battery is on it's way out. The save data will still be there, but the clock will run slower and slower and eventually stop while the Game Boy is off. That is the point where a backup is overdue!